In recent years, application of an organic EL element (an organic electroluminescent element) to a display device such as a flat display and to a light source for an electrophotographic copier and a printer has been investigated. This organic EL element is constituted by providing a first electrode (anode) made of a transparent conductive layer such as ITO (indium tin oxide) on a transparent substrate such as a glass substrate, and by further providing thereon with an organic functional layer including a light emitting layer, and a second electrode (cathode) made of, for example, aluminum in that order. On the circumference of the organic EL element, there are arranged a first electrode (anode) side pickup electrode and a second electrode (cathode) side pickup electrode for connecting the first electrode (anode) and the second electrode (cathode) to an outer circuit or to an internal drive circuit.
It is known that light emission is induced by recombination of an electron with a hole in the organic functional layer when voltage is applied on the EL element to inject an electron from the second electrode (cathode) and a hole from the first electrode (anode), respectively.
An organic EL element is a light emitting element of an electric current drive type which is composed of a very thin organic compound layer (an organic functional layer) including a fluorescent or a phosphorescent light emitting layer sandwiched between a first electrode (anode) and a second electrode (cathode), and emits light by applying an electric current to it. Generally, an organic substance is an insulator, however, it is possible to inject an electric current by making the thickness of the organic layer to be very thin. Further, since an organic EL element can be driven at a voltage as low as 10V or less, and since it is possible to produce light emission with high efficiency, it attracts attention used for a display or a lighting of the future.
As a formation way of a very thin film of an organic compound used for an organic EL element, there are known a dry process method and a wet process method (it is also called a wet coating method).
In the dry process method, a thin film is formed under a high vacuum condition by performing vapor-deposition, for example. In this case, although it excels vey much from the viewpoints of efficiency and quality since it is easy to make a laminated layer structure, on the other hand, vapor-deposition is performed under a high vacuum condition such as 10−4 Pa or less, therefore, the process is complicated and the const becomes high. As a result, it is not necessarily desirable from a viewpoint of production.
On the contrary, in the wet process, there can be adopted various wet processes such as an extrusion coating method, a dip coating method, an ink-jet method, and a printing method. That is, there is an advantage of a low cost because manufacturing under atmospheric pressure is possible. That is, there is an advantage of a low cost because manufacturing under atmospheric pressure is possible. Further, there are advantages of bare generation of unevenness even for a large area since a solution is prepared to make thin film. Therefore, this is a method for forming a thin film currently used to a large extent from the viewpoint of that there is a large merit of cost and manufacturing technology. This can be said a large merit with respect to a cost and a manufacturing technology particularly in illumination application of an organic EL element.
As a production method of an organic EL element, there are known a sheet method which uses a sheet form substrate, and a roll-to-roll method which uses a belt form flexible substrate. However, there is a limit of raising manufacturing efficiency by a sheet method, and since a roll-to-roll method has high potentiality to increase manufacturing efficiency, it is investigated a roll-to-roll method combined with a wet process.
The following method is known: plural first electrodes are formed on a belt form flexible substrate with a roll-to-roll method, then, on these first electrodes are successively applied in a pattern with a hole transport layer forming coating solution, and a light emitting layer forming coating solution with a wet coating method such as an ink-jet method to form a hole transport layer and a light emitting layer (for example. Refer to Patent document 1). However, it is difficult to increase manufacturing efficiency with this method, it will induce nonuniformity of the coating thickness called dry nonuniformity.
The following production method is known as a way of producing an organic electroluminescence panel having a uniform thickness without a defect of dry nonuniformity and with increased manufacturing efficiency by a roll-to-roll method. In this method, an organic functional layer forming coating solution is coated on a continuously conveyed belt form flexible substrate formed thereon a first electrode in a patterned form by using a wet coating mode to coat on the whole surface such as a die coating method (for example, refer to Patent document 2). However, by this method, when the coating solution for forming an organic functional layer is coated to the whole surface by a wet coating method, there will be produced coating unevenness of the organic functional layer induced by the presence of a step difference at a space between one first electrode and an adjacent first electrode since the first electrode is patterned, ant this will result in luminescence nonuniformity. This phenomenon will be easily generated especially at the peripheral area of an electrode.